1. Field of the Invention
The present invention relates to a liquid crystal display device.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, many efforts and studies are being made to develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and electro-luminescence displays (ELDs), as a substitute for CRTs. Of these flat panel displays, LCD devices have many advantages, such as high resolution, light weight, thin profile, compact size, and low voltage power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field into the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
Recently, IPS mode LCD (in-plane switching mode LCD) devices have been proposed. The IPS-LCD device is operated by an in-plane electric field. Accordingly, the IPS mode LCD devices achieve a wide viewing angle compared to LCD devices operated by a vertically induced electric field.
FIG. 1 is a plan view illustrating an array substrate of an IPS mode LCD device according to the related art, and FIG. 2 is a plan view illustrating a color filter substrate of the IPS mode LCD device according to the related art.
Referring to FIGS. 1 and 2, the IPS mode LCD device includes a display region AA and a non-display region NAA. The display region AA transmits light to display images, and the non-display region NAA is a region not to display images and between the display regions AA.
The array substrate includes a gate line 20 and a data line 30 on a first substrate 10 to cross each other to define a sub-pixel region. The sub-pixel region includes red (R), green (G) and blue (B) sub-pixel regions Pr, Pg and Pb. A common line 50 is spaced apart from the gate line 20.
A thin film transistor T is in the sub-pixel region and connected to the corresponding gate and data lines 20 and 30. The thin film transistor T includes a gate electrode 25, a semiconductor layer 40, and source and drain electrodes 32 and 34. The semiconductor layer 40 includes an active layer made of intrinsic amorphous silicon and an ohmic contact layer made of extrinsic amorphous silicon.
A pixel electrode 70 is formed in the sub-pixel region. The pixel electrode 70 is connected to the drain electrode 34 through a connection portion 71. The connection portion 71 contacts the drain electrode 34 through a drain contact hole CH1.
A common electrode 80 is connected to the common line 50. The common electrode 80 and the pixel electrode 70 are alternately arranged in the pixel region.
The color filter substrate includes a color filter layer 16, which includes red, green and blue color filters 16a, 16b and 16c corresponding to the red, green and blue sub-pixel regions Pr, Pg and Pb, respectively, and a black matrix 14. The black matrix 14 blocks light from being emitted from the non-display region.
FIG. 3 is a cross-sectional view illustrating the IPS mode LCD device taken along a line III-III of FIG. 1.
Referring to FIG. 3, the IPS mode LCD device includes a liquid crystal panel 36 including an array substrate 11, a color filter substrate 6 and a liquid crystal layer 15 therebetween, and a backlight unit 90 below the liquid crystal panel 36. A seal pattern (not shown) is used to attach the array substrate 11 and the color filter substrate 6 and formed at peripheral regions of the array substrate 11 and the color filter substrate 6.
The backlight unit 90 includes a plurality of lamps 92 to supply light to the liquid crystal panel 36.
In the array substrate 11, a common electrode 80 is formed on a first substrate 10. A gate insulating layer 45 is formed on the common electrode 80. A data line 30 is formed on the gate insulating layer 45. A passivation layer 55 is formed on the data line 30. A pixel electrode 70 and a connection portion 71 are formed on the passivation layer 55. A first alignment layer 19 is formed on the pixel electrode 70. The data line 30 crosses the gate line (20 of FIG. 1) to define red (R), green (G) and blue (B) sub-pixel regions Pr, Pg and Pb. The common and pixel electrodes 80 and 70 are alternatively arranged in the sub-pixel region.
In the color filter substrate 6, a black matrix 14 is formed corresponding to a non-display region NAA. A color filter layer 16 includes red, green and blue color filters 16a, 16b and 16c corresponding to the red, green and blue sub-pixel regions Pr, Pg and Pb. A second alignment layer 18 is formed on the color filter layer 16.
The black matrix 14 shields the gate line, the data line 30 and the thin film transistor (T of FIG. 1) to prevent light leakage through the non-display region NAA. In a case that the black matrix 14 coincides with the gate line, the data line 30 and the thin film transistor, when misalignment between the array substrate and the color filter substrate occurs, the black matrix 14 may not shield the gate line, the data line 30 and the thin film transistor and the light leakage may occur. To prevent this, the black matrix 14 has a margin so that the black matrix 14 has a width greater than those of the gate line, the data line 30 and the thin film transistor. However, this causes aperture ratio to be reduced.
Recently, to maximize aperture ratio, eliminating the black matrix in the color filter substrate is suggested.
FIG. 4 is a cross-sectional view illustrating an IPS mode LCD device not including a black matrix according to the related art. FIG. 4 shows that a color filter substrate is misaligned with an array substrate. Explanations of parts similar to parts of FIG. 3 may be omitted.
Referring to FIG. 4, the color filter substrate does not include a black matrix. Accordingly, the IPS mode LCD device of FIG. 4 has aperture ratio greater than the IPS mode LCD device of FIG. 3.
When the array substrate 11 and the color filter substrate 6 are attached, the color filter substrate 6 may be misaligned to the array substrate 11 and shifted relatively to the array substrate. For example, the color filter substrate 6 is shifted to the right direction, as shown in FIG. 4. Accordingly, the color filter 16a, 16b and 16c may be located in the corresponding sub-pixel region and the next sub-pixel region in the right direction as well. For example, a right edge portion of the red color filter 16a overlaps the green sub-pixel region Pg, a right edge portion of the green color filter 16b overlaps the blue sub-pixel region Pb, and a right edge portion of the blue color filter 16c overlaps the red sub-pixel region Pr.
In a normal state, the red, green and blue color filters 16a, 16b and 16c function to filter white light emitted from the backlight unit 90, and emit the red, green and blue lights, respectively. However, when the red, green and blue color filters 16a, 16b and 16c are shifted and overlap the pixel regions right thereto, defect such as color mixture occurs. For example, the red color filter 16a is shifted and overlaps the green sub-pixel region Pg. Accordingly, the green sub-pixel region Pg abnormally emits a mixture of a red light and a green light. In similar, mixed colors are emitted in the red and blue sub-pixel regions Pr and Pb. Accordingly, display quality is degraded. Further, this problem may occur to other mode LCD devices not using a black matrix.